Goal → dose + form mapping
The magnesium calculator does not return a single number. It returns a goal-conditional protocol, a daily elemental-mg range, a split-dose count, a recommended form, and acceptable alternates, because the literature for magnesium is goal-specific, not dose-monotonic. The same 400 mg/day looks different depending on whether the target is migraine prevention, blood-pressure reduction, sleep, or repletion.
The mappings the calculator uses, with their evidentiary anchors:
- Migraine prophylaxis → 400–600 mg/day, citrate, split AM/PM. A 2025 dose-response meta-analysis of dietary supplements for migraine prevention reported a mean reduction of 2.51 attacks per month, 0.88 severity points, and 1.66 monthly migraine days with magnesium supplementation versus control (Talandashti et al., 2025, Neurol Sci, PMID 39404918). Twelve weeks of dosing is the conventional minimum before judging response.
- Hypertension adjunct → 300–500 mg/day, citrate, split. The 2025 Hypertension meta-analysis pooled 38 RCTs (N=2,709) at a median elemental dose of 365 mg over 12 weeks. Magnesium reduced systolic BP by 2.81 mm Hg and diastolic BP by 2.05 mm Hg overall, with larger effects (−7.68 / −2.96 mm Hg) in hypertensive individuals on BP medication and in those with hypomagnesemia (Argeros et al., 2025, Hypertension, PMID 41000008). Taurate and glycinate are accepted alternates when GI tolerance or sleep co-targets matter.
- Sleep / anxiety → 200–400 mg/day, glycinate, evening. A systematic review of magnesium for subjective anxiety and stress found a beneficial signal in anxiety-vulnerable samples (mild anxiety, PMS, hypertension) while flagging the underlying evidence as low-quality (Boyle et al., 2017, Nutrients, PMID 28445426). Glycinate is preferred for nighttime use because of its low laxative load.
- Deficiency repletion (override) → 400–600 mg/day, glycinate, split, 8–12 weeks. This bypasses the supplemental upper limit and is meant for serum-confirmed deficiency under clinician guidance.
Why elemental magnesium matters
Every magnesium salt is a compound: a magnesium cation paired with an organic or inorganic ligand. The label dose almost always refers to the entire salt; but only the magnesium fraction is biologically active. The percentage of elemental magnesium varies widely across forms:
- Oxide ≈ 60% elemental
- Citrate ≈ 16%
- Malate ≈ 15%
- Glycinate ≈ 14%
- Taurate ≈ 9%
- L-threonate ≈ 8%
The math: a "500 mg magnesium glycinate" capsule delivers roughly 500 × 0.14 = 70 mg of elemental magnesium. To hit 400 mg/day elemental from glycinate, that is six capsules; not one. A "500 mg magnesium oxide" capsule delivers about 300 mg elemental, but with bioavailability in the 4–10% range, very little of that is absorbed.
The calculator always reports its outputs in mg of elemental magnesium per day. When the form picker is changed, the recommended range does not move; what changes is the implied number of capsules of a typical commercial product. Form selection trades elemental density (oxide is densest, threonate is sparsest) against bioavailability and GI tolerance (oxide is the worst on both, glycinate is the best). Neither end of that trade is universally right; the goal is what arbitrates.
Assumptions and limits
The calculator assumes oral, divided dosing in adults with healthy GI absorption and normal renal function. It does not model:
- IV or IM repletion protocols (used in eclampsia, severe arrhythmia, refractory hypomagnesemia)
- Pediatric dosing
- Pregnancy or lactation specifically
- Polypharmacy interactions beyond the headline separation rules (calcium, tetracyclines, quinolones, bisphosphonates, levothyroxine, PPIs)
The 350 mg/day supplemental upper limit is the IOM ceiling for magnesium from supplements; food magnesium is not capped because dietary forms saturate at the gut. The deficiency override deliberately exceeds the UL and surfaces a clinician-guidance warning. Renal impairment is the hardest contraindication: GFR < 30 raises hypermagnesemia risk dramatically, and the calculator surfaces a hard stop in that range.
Unit conventions
Three unit systems collide in the magnesium literature; the calculator normalizes to the first.
- mg elemental; the biologically active magnesium ion mass. This is the canonical reporting unit and the one used in every output.
- mg of compound; the total salt mass on a supplement label (e.g., "500 mg magnesium citrate"). Multiply by the form's elemental percentage to convert.
- mEq (milliequivalents); common in clinical and IV literature. 1 mEq Mg²⁺ = 12.15 mg elemental. A 2 g IV dose of magnesium sulfate ≈ 16.2 mEq ≈ 197 mg elemental.
When a label, paper, or clinician quotes a number, the first question is which unit they meant.
Why this is documentary, not prescriptive
This page documents how the magnesium calculator picks a dose and a form for a given goal, and what evidence those picks rest on. It is not medical advice. The mapping is built from goal-specific RCT and meta-analysis data, but the trial populations rarely match any individual reader's situation precisely, the form-comparison literature is thinner than the dose-response literature, and renal status, polypharmacy, and serum baseline all change the right answer in ways a goal toggle cannot capture.
Use the output as a starting frame for a conversation with a clinician; especially if magnesium is being layered on antihypertensives, anti-arrhythmics, or anything renal. Every PMID on this page was verified live against PubMed metadata before publication by the same INT-01 citation guardrail that gates the calculators on this site.